ovn-northd: Sort options in put_dhcp(v6)_opts.

ovn-northd: Sort options in put_dhcp(v6)_opts.

The order of the options in the packet generated by ovs-controller
depends on the hash function.  I believe that murmur hash (our default)
produces different outputs depending on the endianness of the system.
Also, if SSE4.2 is enabled at build time, we use CRC32 for hashing which
gives different results even on x86.

This causes one unit test to fail on big endian or with SSE4.2:

ovn -- dhcpv4 : 1 HV, 2 LS, 2 LSPs/LS

This commit fixes the problem in ovn-northd by always sorting dhcp
options inside the logical flow put_dhcp(v6)_opts action.

Reported-at: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=840770
Suggested-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Ben Pfaff <blp@ovn.org>